The invention relates to helicopter storage and shipment and, more particularly, to prevention of undesired upward rotation of helicopter blade pitch housings and attached blades during out-of-use periods.
Helicopter blades, during operation, are rotated basically in a plane of rotation which is nominally a horizontal plane. A helicopter blade is typically attached to a blade pitch housing (enabling controlled adjustment of blade pitch) which is attached to the rotor assembly, rotation of which produces blade rotation. While rotating, displacement or rotation of the blades upward from the plane of rotation is limited by the effects of centrifugal force. When out-of-use (e.g., parked, stored, in shipment) no centrifugal forces act on the blades and the blades and pitch housings are permitted to flap downward (called “droop”) a small amount under the influence of gravity. Their weight is supported by a droop stop mechanism. When out-of-use the blades are typically unrestrained from a range of upward rotation (e.g., rotation in a vertical plane, about the connection point to the rotor assembly). Such upward rotation may be caused by wind forces while parked or stored, or by sudden altitude or attitude changes or other forces experienced during shipment of a helicopter in a transport aircraft or while being towed on the ground, for example.
During shipment or storage the blades of a helicopter may be folded (i.e., some or all blades positioned toward the tail or nose of the helicopter) while each blade still remains attached to its respective blade pitch housing which remains attached to the rotor assembly (blade folding is further described in U.S. Pat. No. 6,783,327, having a common assignee). Whether or not the blades are folded, upward rotation of a blade pitch housing, during shipment for example, is undesirable and may result in damage to the blade, the blade pitch housing or other components of the rotor blade mechanism, or to the interior area of a transport aircraft immediately above the stowed helicopter. For present purposes, uncontrolled upward rotation of a blade pitch housing (i.e., with its attached blade) of a helicopter which is not in use will be termed “flap”. Correspondingly, undesired upward rotation of a blade may be termed “blade flap”. Prior mechanisms and techniques have not provided effective limitation of blade flap or have been subject to limitations regarding cost, complexity, reliability, durability or other disadvantages.
Objects of the present invention are to provide new and improved lock units and methods, which may provide advantages such as the following:
ease of installation;
reliable operation;
absence of required aircraft modification;
cost effectiveness;
low complexity of construction;
durability; and
ease of removal.